Old topic I know, but thought I'd post my experience with a particularly loud and annoying squeak coming from somewhere in my dashboard. After months of stuffing bits of foam into various holes around the dash and windscreen, with no success, I happened to notice one day when poking under the bonnet that the battery was slightly loose - and low and behold, as I moved it slightly, a really annoying squeak appeared! Tighten up the bolts, and apply a bit of grease, and low and behold, squeak has gone. Amazing how the noise travels into the cabin - I was sure it was the dash making the noise.
Now if I could only get rid of the rattles...!
May not be the solution for every squeak, but could worth checking out just in case. Hope it helps out someone.